Just some advice from an old technician, who knows that things often can go wrong. :-) Use an opto-isolator to read off of whatever port you choose to use. The isolator will only load the port with a simple led, and will have a few thousand volts of "insulation" between the port and the actual relays. You will blow out your computer, if for some reason (lightning, rats chewing wires, idiot janitors,etc) causes a short in the bell relay and pumps 110 or 220 vac into your port. Opto-isolators are very cheap and easy to setup. Do a google search for "opto-isolator computer port".